| The stochastic responses of the Santa Felicia earth dam to spatially varying earthquake ground motion (SVEGM) are analyzed. A space-time earthquake ground motion model that accounts for both coherency decay and seismic wave propagation is used to specify the support motions, and the results are compared with those for various simplified excitations. In addition, a preliminary reliability analysis using the Mohr-Coulomb strength criterion is performed. The effects of propagation speed and direction for SV/P and SH waves and different coherency models on the responses of the dam are also investigated. Finally, techniques to simplify the excitation for use with simplified mechanical models of the dam are presented.; The Santa Felicia dam is represented as a three-dimensional inhomogeneous finite element model using the I-DEAS VI.i computer program. The variation of shear modulus with depth from the crest due to confining pressure is taken into account. Finite element-based random vibration analysis is performed and the statistical moments of the displacement, strain and stress responses are computed. Statistical moments of the maximum shear stress, which is non-linearly related to the Cartesian stresses, are computed using Monte Carol simulation as well as an approximate first order second moment method.; The results of the study indicate that the effect of SVEGM is significant, especially on the stress response of stiff material near the base of the dam. The assumption of fully coherent support motions is found to slightly over-estimate the displacement and strain responses but significantly under-estimate the stress response near the base. The wave passage effect is not as significant as the coherency decay when the ground displacements are not highly coherent. The sensitivity of the stress response to different coherency functions at the base can be dramatic. For simplified analysis, a 2-D shear beam model should be capable of yielding good results at locations distant from the base with a suitably modified seismic excitation. For computing the stress response in stiff material near the base, a 3-D finite element model is required, but costly dynamic analysis can be avoided if the ground displacements are not highly coherent; a pseudo-static analysis suffices in this case. |
